Use is/is not to check for None in python code.

While reviewing a patch sent to the mailing list, I noticed there are few
places where python code checks if a variable is 'None' or not by using the
comparison operators '==' and '!='.  PEP8[1], which is used as coding standard
in GDB coding standards, recommends using 'is' / 'is not' when comparing to a
singleton such as 'None'.

This patch proposes to change the instances of '== None' by 'is None' and
'!= None' by 'is not None'.

[1] https://www.python.org/dev/peps/pep-0008/

gdb/doc/ChangeLog:

	* python.texi (Writing a Pretty-Printer): Use 'is None' instead of
	'== None'.

gdb/ChangeLog:

	* python/lib/gdb/FrameDecorator.py (FrameDecorator): Use 'is None' instead of
	'== None'.
	(FrameVars): Use 'is not None' instead of '!= None'.
	* python/lib/gdb/command/frame_filters.py (SetFrameFilterPriority): Use 'is None'
	instead of '== None' and 'is not None' instead of '!= None'.

gdb/testsuite/ChangeLog:

	* gdb.base/premature-dummy-frame-removal.py (TestUnwinder): Use
	'is None' instead of '== None' and 'is not None' instead of
	'!= None'.
	* gdb.python/py-frame-args.py (lookup_function): Same.
	* gdb.python/py-framefilter-invalidarg.py (Reverse_Function): Same.
	* gdb.python/py-framefilter.py (Reverse_Function): Same.
	* gdb.python/py-nested-maps.py (lookup_function): Same.
	* gdb.python/py-objfile-script-gdb.py (lookup_function): Same.
	* gdb.python/py-prettyprint.py (lookup_function): Same.
	* gdb.python/py-section-script.py (lookup_function): Same.
	* gdb.python/py-unwind-inline.py (dummy_unwinder): Same.
	* gdb.python/python.exp: Same.
	* gdb.rust/pp.py (lookup_function): Same.

2 files changed, 7 insertions, 7 deletions

diff --git a/gdb/python/lib/gdb/FrameDecorator.py b/gdb/python/lib/gdb/FrameDecorator.py
index 1f4b2ca..69a0a9a 100644
--- a/gdb/python/lib/gdb/FrameDecorator.py
+++ b/gdb/python/lib/gdb/FrameDecorator.py
@@ -117,7 +117,7 @@ class FrameDecorator(object):
         # address.  If GDB detects an integer value from this function
         # it will attempt to find the function name from minimal
         # symbols via its own internal functions.
-        if func == None:
+        if func is None:
             pc = frame.pc()
             return pc
 
@@ -270,7 +270,7 @@ class FrameVars(object):
         except RuntimeError:
             block = None
 
-        while block != None:
+        while block is not None:
             if block.is_global or block.is_static:
                 break
             for sym in block:
@@ -295,12 +295,12 @@ class FrameVars(object):
         except RuntimeError:
             block = None
 
-        while block != None:
-            if block.function != None:
+        while block is not None:
+            if block.function is not None:
                 break
             block = block.superblock
 
-        if block != None:
+        if block is not None:
             for sym in block:
                 if not sym.is_argument:
                     continue
diff --git a/gdb/python/lib/gdb/command/frame_filters.py b/gdb/python/lib/gdb/command/frame_filters.py
index 91e8ca2..97488ca 100644
--- a/gdb/python/lib/gdb/command/frame_filters.py
+++ b/gdb/python/lib/gdb/command/frame_filters.py
@@ -372,7 +372,7 @@ class SetFrameFilterPriority(gdb.Command):
 
     def invoke(self, arg, from_tty):
         command_tuple = self._parse_pri_arg(arg)
-        if command_tuple != None:
+        if command_tuple is not None:
             self._set_filter_priority(command_tuple)
 
 
@@ -453,7 +453,7 @@ class ShowFrameFilterPriority(gdb.Command):
 
     def invoke(self, arg, from_tty):
         command_tuple = self._parse_pri_arg(arg)
-        if command_tuple == None:
+        if command_tuple is None:
             return
         filter_name = command_tuple[1]
         list_name = command_tuple[0]